FIG. 1 shows a pressure measurement pod 10. In the pod 10, air chamber 45 is in communication with an air port 12 and air line 40 that can be connected to a pressure transducer (not shown). Fluid flows through a fluid chamber 60 between an inlet line 35 connected to an inlet port 70 and out of the fluid chamber 60 through an outlet port 72 into an outlet line 15. The pressure of the fluid in the fluid chamber 60 displaces a diaphragm 25 until the air chamber 45 and fluid chamber 60 are at equilibrium, which is preferably the situation when the air and fluid chambers 45 and 60 are at equal pressure.
The pod 10 is primarily made of two parts, a fluid-side shell 30 and an air-side shell 17, that, together, form an enclosure 5 that defines the fluid and air chambers 60 and 45. The ratio of the minimum to the maximum volume of the air chamber 45, including the volume of the line 40 and port 12, is proportional to the total pressure variation that can be measured by the transducer attached to the line 40. The fixed volume defined by the line 40 and port 12 serves as a limit on this ratio and therefore limits the pressure range that can be measured. Another feature of the pod 10 is that the fluid shell must be formed by a mold that has more than two parts, because of the inlet and outlet ports 70 and 72 and the recess that helps define the fluid chamber 60. Since molds with more than two parts are more expensive to design and make, this is a disadvantage.
Another feature of the pod 10 is the orientation of the inlet and outlet lines 35 and 15 owing to those of the inlet and outlet ports 70 and 72. The orientations require the pod 10 be placed in a straight run of tubing, which can make it difficult to design a compact fluid circuit assembly in which the pod is used. Yet another feature is the use of an intermediate line 40 between the transducer and the pod 10, which makes the pod assembly larger, requires more parts to be assembled, and has more seals which may fail. Another feature of prior art pods in general is the use of diaphragms that are more permeable than may be desirable. Also, the attachment between the blood side shell 30 and the air side shell 17 may be made by a compression seal (details not shown) or by another means of attachment, but in any event, may require additional steps to seal the diaphragm within.